Prolonged stimulation of the adrenals by corticotropin suppresses hepatic low-density lipoprotein and high-density lipoprotein receptors and increases plasma cholesterol.

Abstract

Pituitary ACTH has been shown to strongly stimulate adrenal receptors for low-density lipoprotein (LDL) and high-density lipoprotein (HDL) scavenger receptor class B type 1(SR-BI) to provide precursor cholesterol for glucocorticoid synthesis. The present study aimed to determine the effects of ACTH on hepatic cholesterol metabolism and plasma lipoproteins. Treatment of Sprague Dawley rats or normal C57BL/6J mice with ACTH for 3.5 d reduced hepatic SR-BI and LDL receptors. Simultaneously, cholesterol in plasma LDL and HDL was increased. None of these effects could be reproduced using glucocorticoids instead of ACTH, and they were abolished in adrenalectomized rats, indicating an obligate role of the adrenals for the effects of ACTH observed in the liver. When ACTH was given to LDL receptor-deficient mice, plasma LDL did not increase and the increase in HDL cholesterol remained, as did the suppression of hepatic SR-BI. Our data show that prolonged ACTH treatment suppresses hepatic SR-BI and LDL receptors in vivo in rodents, resulting in elevated plasma HDL and LDL. The adrenals are obligate for these effects, suggesting that ACTH releases some factor(s) that suppresses hepatic LDL and SR-BI receptors. Hypothetically, this novel mechanism would further promote channeling of cholesterol to the adrenals in situations of prolonged stress.